<template>
  <div class="todo-footer" v-show="total">
    <label>
      <input type="checkbox" :checked="isAll" @change="checkAll" />
    </label>
    <span>
      <span>已完成{{ doneTotal }}</span> / 全部{{ total }}
    </span>
    <button class="btn btn-danger" @click="clearAll">清除已选中任务</button>
  </div>
</template>

<script>
export default {
  name: 'MyFooter',
  props: ['todos'],
  computed: {
    total() {
      return this.todos.length
    },
    doneTotal() {
      // reduce 函数：就是循环一遍 todos 这个数组，pre 相当于循环中的 i
      return this.todos.reduce((pre, todo) => pre + (todo.done ? 1 : 0), 0) // 0 是初始值
    },
    isAll() {
      // 选中所有的 并且 有选项
      return this.doneTotal === this.total && this.total > 0
    },
  },
  methods: {
    checkAll(e) {
      // e.target.checked 的值是true 或 false
      this.$emit('checkAllTodo', e.target.checked)
    },
    clearAll() {
      this.$emit('clearAllTodo')
    }
  }

}
</script>

<style scoped>
/*footer*/
.todo-footer {
  height: 40px;
  line-height: 40px;
  padding-left: 6px;
  margin-top: 5px;
}

.todo-footer label {
  display: inline-block;
  margin-right: 20px;
  cursor: pointer;
}

.todo-footer label input {
  position: relative;
  top: -1px;
  vertical-align: middle;
  margin-right: 5px;
}

.todo-footer button {
  float: right;
  margin-top: 5px;
}
</style>

